1. Field of the Invention
The present invention relates generally to the field of self-locking fasteners, and more specifically to a bolt apparatus for mounting a lawn mower blade which can be quickly and safely disengaged from above the blade shroud by one person, said bolt apparatus including a bolt head for supporting the blade, a shank portion extending through the drive tube in the mounting spindle, and a threadless fastening end with a circumferential channel engaged by a bolt lock assembly, said bolt lock assembly comprising a cylindrical sleeve having opposing angled pin slots, a locking pin in each slot which laterally enters the bolt circumferential channel, a spring-loaded washer for biasing the pins into the slots, and a release member slidingly fitted around the sleeve for pushing the pins out of their slots and out of the channel, against the resistance of the spring-loaded washer, to release the bolt to drop out of the drive tube.
2. Description of the Prior Art
There have long been self-locking fasteners for various applications where either very reliable fastening or the ability to quickly disengage is needed.
Ockert, U.S. Pat. No. 3,180,390, issued on Apr. 27, 1965, teaches a locking bolt for connecting aircraft linkages, having an engaging end which protrudes beyond the linkages. The bolt has a diametrically oriented bore through its engaging end which contains two metal balls. These balls can be spread apart to extend half-way out of the holes and into a containing ring when the bolt is installed, to prevent the bolt from sliding out of its bore. An axial passageway within the bolt contains a spring-loaded, sliding shaft having a beveled, expanded section for camming the balls into and out of the locking position. The sliding shaft extends into a slot in the head of the bolt so that a screw driver inserted into the slot moves the shaft and cams the balls into an unlocked position. A castellated nut and cotter pin further secure the bolt. A problem with Ockert is that the entire locking apparatus is contained in the bolt itself, so that if the bolt fatigues or deforms, the entire apparatus must be replaced. Another problem is that, should the locking mechanism become jammed, the working elements are not accessible for servicing. Finally, the elaborate cam structure of Ockert would be costly to manufacture.
Herrmann, U.S. Pat. No. 3,302,960, issued on Feb. 7, 1967, discloses a locking device designed for virtually instantaneous release, designed for rocket launching applications. A shaft having a circumferential channel with beveled side walls fits into a bore in a member having a three radially oriented passageways extending through opposing walls of the bore. Each passageway contains two metal balls, each essentially matching the diameter of the passageway. A spring-loaded sleeve slidingly surrounds the outer openings of the passageways, has an inwardly directed flange of a width equal to the passageway diameter, and forms part of the passageway walls. The passageway is of a length such that both balls can fit within it only if the inner ball extends into the channel. Sliding the sleeve moves the flange, widens the outer portion of the passageway, and thereby permits the outer ball to move to one side and leave room for the inner ball to ride out of the channel, thereby freeing the shaft. A problem with Herrmann is that the passageways and channel must be cut to close tolerances to operate properly, making the device costly. And if one of the balls were lost during servicing, an exact duplicate would have to be found to fit properly.
McKay, U.S. Pat. No. 3,390,712, issued on Jul. 2, 1968, teaches a self-locking fastener similar to that of Ockert. The McKay fastener is a bolt containing an axial passageway and an elongate cam member. The cam member drives two spike members outward through radial bores to engage the outer face of the rearmost workpiece being fastened. An end of the cam member is exposed for operating the lock. McKay recites that a primary inventive feature is the making of line contact between the radially expanding members and the cam surfaces. A problem with McKay is that, once again, the entire locking mechanism is contained in the fastener itself, and if the fastener becomes worn or damaged, the user faces the expense of replacing the entire mechanism. Also, the mechanism is not readily serviceable.
Berte, U.S. Pat. No. 4,908,916, issued on Mar. 20, 1990, discloses a connecting pin device with a safety lock for coupling a tractor to a wagon. A cylindrical pin has a circumferential channel at one end which fits into a tubular locking mechanism having a series of balls positioned circumferentially around its exterior, and a hole adjacent to each ball. The mechanism receives the pin to a depth that aligns the channel with the holes. An outer sleeve having an interior cam surface is biased to slide axially along the mechanism to cam the balls part way through the holes and engage the channel. Pushing the sleeve in the opposite direction against the biasing releases the balls to move radially outward, unlocking the pin. A problem with Berte is that the locking ball arrangement is relatively expensive to manufacture.
Knecht, U.S. Pat. No. 3,793,685, issued on Feb. 26, 1974, teaches a coupling apparatus for the mooring of boats. Knecht provides an anchor member for bolting to a dock, having a protruding stud, and a stud locking mechanism at the end of the bow line. The structure of Knecht is much like that of Berte, providing a series of balls positioned adjacent to holes around the locking member, and an outer sleeve with a cam interior. Axially sliding the sleeve in one direction cams the balls through the holes and part way into the channel, to lock the stud in the mechanism. A spring-loaded plunger inside the mechanism pushes the stud out when the sleeve is slid in the opposite direction to disengage the lock. A problem with Knecht is that the elements of the structure must be carefully positioned to operate properly, and the ball arrangement is costly.
Lew, U.S. Pat. No. 4,507,034, issued on Mar. 26, 1985, discloses an expandable bushing and locking device for joining workpieces together. The structure is much like McKay in that a bolt is provided having an axial passageway and a sliding cam member within the passageway to drive locking elements radially outward, to protrude on opposing sides of the bolt. The problems presented by Lew are the same as those identified for McKay.
Olivieri, U.S. Pat. No. 4,913,610, issued on Apr. 3, 1990, teaches a device for preventing a wheel from slipping off an axle on which it is mounted, while permitting the wheel to rotate freely. A channel is provided around the end of the axle and an annular hub member is placed over the channel adjacent the wheel. Then two securing plates radially slide into grooves in the hub member, and present concave edges to engage the axle channel. A problem with Olivieri, if applied to lawn mower blade bolts, is that it is by design difficult to remove, so that blade replacement would be unduly time-consuming and inconvenient.
It is thus an object of the present invention to provide a lawn mower bolt and lock apparatus which can be removed by a single person from above the blade shroud, to prevent injury by the blade.
It is another object of the present invention to provide such an apparatus which locks the bolt reliably and rotatably within the shroud spindle and permits quick and easy releasing and engaging of the bolt.
It is still another object of the present invention to provide such an apparatus wherein the locking elements are located in an assembly separate from the bolt, so that the bolt can be replaced without replacing the locking elements.
It is finally an object of the present invention to provide such an apparatus which is sturdy, easy to service and relatively inexpensive to manufacture.